01 - Heat olive oil and 1 tablespoon butter in a large heavy-bottomed skillet over medium heat. Cook onions until translucent, about 3 minutes, then stir in garlic and cook 1 minute more.
02 - Add sliced mushrooms and cook, stirring occasionally, until golden and liquid evaporates, about 8 minutes. Season with ¼ teaspoon salt and a pinch of pepper. Set aside half for garnish.
03 - Add Arborio rice to the skillet and toast, stirring constantly, until grains are translucent at edges, about 2 minutes.
04 - Pour in white wine and cook, stirring, until almost fully absorbed.
05 - Add 1 cup warm broth and stir gently until mostly absorbed. Continue adding broth ½ cup at a time, stirring frequently and waiting for absorption before adding more, until rice is creamy and al dente, 18 to 22 minutes.
06 - Reduce heat. Stir in remaining 2 tablespoons butter, Parmesan cheese, heavy cream, and half the chopped parsley. Adjust seasoning with remaining salt and pepper.
07 - Spoon risotto into bowls. Top with reserved sautéed mushrooms and garnish with remaining parsley. Serve immediately.